Hot air generator using a gaseous fuel

ABSTRACT

A hot air generator using a gaseous fuel. The generator comprising a tubular body carrying air to be heated, a mixing tube carrying gaseous fuel and primary air to a burner located at the downstream end of the mixing tube. Radially fins or blades are disposed in the burner constituting a centrifugal fan. A combustion chamber is generally coaxially arranged in the tubular body generally downstream of the centrifugal fan means. The downstream wall of the burner formed by a heat grid permitting the passage of the fuel mixture for forming a flame on its surface.

United States Patent 11 1 1111 3,752,644 Arnal Aug. 14, I973 HOT AIR GENERATOR USING A GASEOUS 3,358,736 12/1967 Reed et al 431/168 x FUEL Inventor: Louis Henri Pierre Arnal, La

Celle-Saint-Cloud, France Assignee: Societe Anonyme Sefacal, Paris,

France Filed: Dec. 23, 1971 Appl. No.: 211,391

US. Cl. 432/222, 431/353 Int Cl F23] 5/02 References Cited UNITED STATES PATENTS 8/1966 Safford 263/19 A Primary Examiner-Edward G. Favors Attamey-Nichol M. Sandoe et al.

[57] ABSTRACT A hot air generator using a gaseous fuel. The generator comprising a tubular body carrying air to be heated, a mixing tube carrying gaseous fuel and primary air to a burner located at the downstream end of the mixing tube. Radially fins or blades are disposed in the burner constituting a centrifugal fan. A combustion chamber is generally coaxially arranged in the tubular body generally downstream of the centrifugal fan means. The downstream wall of the burner formed by a heat grid permitting the passage of the fuel mixture for forming a flame on its surface.

11 Claims, 2 Drawing Figures BACKGROUND OF THE INVENTION The present invention relates to a hot air generator using a gaseous fuel, of the type comprising an electric motor driving a fan, a tube for mixing the injected gas eous fuel and the primary air, arranged along the axis of the fan, a combustion chamber, the downstream portion of the said mixing tube extending into the combustion chamber and forming a burner, and a casing formed by a tubular body, the fan and the mixing tube being centered at one end of the tubular body, the combustion chamber occupying the central axial portion of the tubular body. Such a generator is disclosed in French Pat. No. 1,555,581 and Patents of Addition Nos. 94,511 and 95,410.

SUMMARY OF THE INVENTION An object of the present invention is to use the rotation of the. burner, for the purpose of setting the fuel mixture into movement.

According to the present invention, the burner of the generator comprises a body fixed for rotation with the mixing tube, radial fins fixed on the internal wall thereof, forming a centrifugal fan, the upstream wall of the burner being provided with an orifice for communication with the mixing tube.

According to a preferred embodiment of the present invention, the downstream wall of the casing comprises a heating grid adapted to retain or anchor the flame.

According to a feature of the present invention, the burner body is advantageously constituted by a moulded, stamped or machined metal cylinder.

According to another feature of the invention, the burner is housed in the interior of the combustion chamber, the external diameter of the cylinder being less than the internal diameter of the chamber.

The fins or blades are arranged along radial planes of the cylinder, there being a sufficient number to form a centrifugal fan.

According to another feature of the present invention, the heating grid, preferably of circular shape, is formed either by a metal gauze or by a moulded plate provided with slots, or by means permitting the passage of the fuel mixture and the formation of the flame on its surface.

According to another feature of the invention, the central part of the downstream face of the burner body is constituted by a non perforate element preferably in the form of a circular disc, which prevents the backfire of flame into the axis of the system. Such backfires are produced owing depressions existing at the center of the face since the centrifugal fan formed by the fins has a tendency to suck in the surrounding fluid in the axial zone of the said fan.

BRIEF DESCRIPTION OF THE INVENTION An embodiment of the invention is described below by way of example, reference being made to the accompanying drawings, in which:

FIG. 1 is a partial view in longitudinal section of a hot air generator with a burner fixed for rotation with the mixing tube according to the present invention and FIG. 2 is an end view taken along the line IIII in FIG. 1 of the burner of the generator.

DESCRIPTION OF A PREFERRED EMBODIMENT FIGS. 1 and 2 show a mixing tube 6, a burner 7, a fan 8, a tubular body 1 forming an outer casing and a combustion chamber 2.

The tube 6 is formed by the shaft of an electric motor (not shown) for driving the fan 8 the mixing tube 6, the burner 7 and the fan 8 are rigidly fixed together for rotation.

The burner 7 is formed by a metal cylindrical body providing a casing radial fins 7a are fixed to the internal wall of the body the upstream face 7b of the cylindrical body has an axial aperture 70 provided with a pcripheral flange 7d which is inset or welded on the outer wall of the mixing tube 6. The central portion of the downstream wall of the cylindrical body of the burner 7 is formed by a solid or non perforate circular disc 7c and the peripheral portion by a metal grid 17 which permits the passage of the fuel mixture for forming a flame on its surface.

The generator operates in the following manner The mixture of primary air and gaseous fuel is drawn into interior of the mixing tube 6 by means of the centrifugal fan formed by the radial fins 7a of the burner 7. This mixture is discharged into the interior of the combustion chamber 2 in the direction indicated by the arrows F l it is ignited by a pilot flame (not shown) under conditions such that the flame is initiated on contact with the grid 17. The pilot light may be replaced by an electric ignition device.

The air, drawn in and pulsated by the fan 8 is carried in the direction shown by the arrows F2 in the annular space formed between the combustion chamber 2 and the tubular body 1. The products of combustion become mixed with this air pulsated by the fan 8, following which the mixture of hot air thus obtained is carried into the space to be heated.

The essential advantage of the arrangement which has just been described resides in the fact that the primary air and the fuel gas are sucked-in through the mixing tube 6.

For this reason, it is not necessary to make use of the pressure of the fuel gas to propel the primary air necessary for combustion.

It is therefore possible to use gases which have a low vapour tension, such as butane, or which is distributed in systems under very low pressure, such as town gas, natural gas, etc.

The form and the dimensions of the burner 7 as well as the speed of rotation of the mixing tube-burner-fan assembly are chosen as a function of the desired thermal output of the burner, and on the aeration rate of primary air which is to be given to the combustion. This aeration rate is much more stable than that'of air induction burners since it is substantially independent of the gas pressure which may be very low.

What I claim is:

l. A hot air generator using a gaseous fuel, comprising a tubular body carrying air to be heated, a mixing tube for carrying a mixture of gaseous fuel and primary air to a burner located at the downstream end of the mixing tube and in communication therewith, the burner being mounted for rotation with the mixing tube, a combustion chamber generally coaxially arranged in the tubular body, and a centrifugal fan means comprising a plurality of radial blades fixed to the inner wall of the burner, said centrifugal fan means being operatively disposed between the mixing tube and the combustion chamber generally coaxially thereto.

2. A hot air generator in accordance with claim 1, wherein the burner comprises an upstream wall including an orifice in communication with the mixing tube, and a downstream wall formed by heating grid means permitting the passage of the fuel mixture for forming a flame on its surface.

3. A hot air generator in accordance with claim I,

wherein the burner is formed as a cylindrical metal body.

4. A hot air generator-in accordance with claim 1,

wherein the burner is disposed in the combustion chamber.

5. A hot air generator in accordance with claim 2, wherein the heating grid means comprises a wire gauze. 6. A hot air generator in accordance with claim 2, wherein the heating grid means is formed as a slotted molded plate.

7. A hot air generator in accordance with claim 2, wherein the central portion of the downstream wall of the burner is a non perforate element.

8. A hot air generator in accordance with claim 7,

tube for circulating air to be heated. 

1. A hot air generator using a gaseous fuel, comprising a tubular body carrying air to be heated, a mixing tube for carrying a mixture of gaseous fuel and primary air to a burner located at the downstream end of the mixing tube and in communication therewith, the burner being mounted for rotation with the mixing tube, a combustion chamber generally coaxially arranged in the tubular body, and a centrifugal fan means comprising a plurality of radial blades fixed to the inner wall of the burner, said centrifugal fan means being operatively disposed between the mixing tube and the combustion chamber generally coaxially thereto.
 2. A hot air generator in accordance with claim 1, wherein the burner comprises an upstream wall including an orifice in communication with the mixing tube, and a downstream wall formed by heating grid means permitting the passage of the fuel mixture for forming a flame on its surface.
 3. A hot air generator in accordance with claim 1, wherein the burner is formed as a cylindrical metal body.
 4. A hot air generator in accordance with claim 1, wherein the burner is disposed in the combustion chamber.
 5. A hot air generator in accordance with claim 2, wherein the heating grid means comprises a wire gauze.
 6. A hot air generator in accordance with claim 2, wherein the heating grid means is formed as a slotted molded plate.
 7. A hot air generator in accordance with claim 2, wherein the central portion of the downstream wall of the burner is a non perforate element.
 8. A hot air generator in accordance with claim 7, wherein the central portion is formed as a circular disc.
 9. A hot air generator in accordance with claim 3, wherein the outer diameter of the cylinder forming the burner is less than the diameter of the combustion chamber.
 10. A hot air generator in accordance with claim 1, wherein the combustion chamber is formed by a hollow tube.
 11. A hot air generator in accordance with claim 1, wherein a fan is mounted on the exterior of the mixing tube for circulating air to be heated. 